As today's deep wells challenge the bounds of pressure and temperature, accurate reservoir testing has become essential to mitigate production risk. The information contained in a series of downhole pressure transient measurements and representative reservoir fluid samples can make or break a prospect’s potential. The Quartet-HT system maintains well integrity while testing safely, accurately, and efficiently at the extremes of the well environment. The multicycle and single-trip features provide operational efficiencies that can reduce rig time and risk. The high temperature capabilities allow operators to isolate, control, measure, and sample closer to the high temperature reservoir for better test results and more accurate reservoir characterization.